Some devices require padded images in order to prevent CFE from flashing them
to the wrong offset.
For small flashes (4/8) this is no big deal, but for larger flashes (16/32) this
implies 8 and 16 MB images, which is way too large and some devices aren't
capable of flashing them through sysupgrade.
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>